Method of manufacturing an insulated electrical conductor



Sept. 22, 1970 B. E. ASH 3,530,018

METHOD OF MANUFACTURING AN INSULATED ELECTRICAL CONDUCTOR Filed Oct. 24. 1966 Inventor BERNARD 5 A Home y ted tates U.S. Cl. 156-54 7 Claims ABSTRACT OF THE DISCLOSURE A strip of insulating material is formed into a tube about a conductor with adhesive applied to an edge between overlapping portions. The insulated conductor is passed around a pulley with the overlapping portlons pressed between the pulley and conductor until the adhesive sets. An elongated stepped die opening tapers mto a round opening to form the tube with overlapping edges.

This invention relates to a method of manufacturing an insulated electrical conductor, and particularly an electrical conductor insulated with paper.

In known methods of insulating conductors with, for example, paper, adhesive is applied to one edge of a strip of paper which is then formed into a tube around the conductor with'the edges of the strip overlapping.

In order to hold the paper strip round the conductor while the adhesive is setting the conductor is drawn through a circular die for the setting time. However, longitudinal force applied to the paper strip during this process stresses and tends to tear the paper.

According to the present invention there is provided a method of manufacturing an insulated electrical conductor, which comprises the steps of applying an adhesive coating lengthwise to at least a portion of one face of a strip of insulating material, then forming the strip into a tube round the electrical conductor with the edges of the strip overlapping and with said coating between the overlapping portions, and thereafter passing the conductor round a rotating pulley with the overlapping portions pressed between the conductor and the circumference of the pulley for at least the time period required for the coating to set sufliciently to prevent the overlapping portions from springing apart.

An embodiment of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 shows an embodiment of apparatus for manufacturing an insulated electrical conductor;

FIG. 2 shows in more detail a die shown in FIG. 1.

Referring now to the accompanying drawings, a strip of insulating material 1, for example paper, is coated with adhesive along the edge 2 of its uppermost surface by moving it past a screw fed extruder 3 for applying an adhesive coating from a reservoir tube 4; a suitable adhesive substance in the case of paper is a starch based paste. The rate of extrusion of the adhesive substance is adjusted to correspond to the rate at which the insulating strip is moving.

The insulating strip is then passed together with an electrical conducting wire 5 to the inlet 6 of a die 7. The die is shown in greater detail in FIG. 2. The inlet of the die is of oblong shape with the shorter sides of the oblong well rounded and with a step in one of the longer sides. The insulating strip is inserted in the inlet so that the side with the step faces towards the coated edge of the strip. The passage in the die tapers towards a circular outlet 8, so that an insulating strip, on being fed through this passage together with a wire, is gradually formed into a tube round the wire and emerges with the coated edge portion 2 overlapping a portion of the strip, the coating being between the overlapping portions adjacent the other edge of the strip.

The angular position of the residual strip near the circular outlet is chosen so the seam in the emerging paper tube is positioned between the wire and a pulley 9, which rotates in the direction indicated by the arrow in FIG. 7 and which is used as a capstan to haul the insulating strip and wire through the die. The diameter of the capstan and the number of turns of insulated wire round the capstan are chosen so that each portion of insulated wire makes contact with the capstan, i.e. pressure is applied to the seam in the paper tube for a time period at least equal to the time required for the adhesive to set. The distance between the outlet from the die and the capstan is preferably kept as short as possible to reduce the risk of unrolling of the paper tube before it reaches the capstan.

What I claim is:

1. A method of manufacturing an insulated electrical conductor, which comprises the steps of applying an adhesive coating lengthwise to an edge portion of one face of a strip of insulating material, then forming the strip into a tube round the electrical conductor with the edges of the strip overlapping to form a seam and with said coating between the overlapping edges, and thereafter passing the conductor round a rotating pulley with the overlapping edges positioned to be pressed between the conductor and the circumference of the pulley for at least the time period required for the coating to set sufficiently to prevent the overlapping edges from springing apart.

2. A method as claimed in claim 1, including applying the coating with an adjustable extruder, wherein the rate of extrusion is regulated to correspond to the speed of the pulley.

3. A method as claimed in claim. 1 wherein said insulating strip is of paper.

4. A method as claimed in claim 3, wherein the coating comprises a starch based paste.

5. A method as claimed in claim 1 wherein said rotating pulley is a capstan hauling the insulated wire.

6. Apparatus for manufacturing an insulated electrical conductor comprising means for applying an adhesive coating lengthwise to an edge portion of one face of a strip of insulating material, means for forming the strip into a tube around the electrical conductor with the edges of the strip overlapping to form a seam and with said coating between the overlapping edges, and. rotating pulley means drawing the conductor from the forming means with the overlapping edges positioned to be pressed between the conductor and the circumference of the pulley for a time required for the coating to set and prevent the overlapping edges from separating.

7. The apparatus of claim 6 wherein said forming means includes a die having an elongated opening at one end with rounded short sides and a circular opening at the other end, said elongated opening including a step in one of the long sides to position the edges of the strip in an overlapping relation between said conductor and pulley.

References Cited UNITED STATES PATENTS 1,945,709 2/1934 Sirnons 156-54 2,494,050 1/1950 Loucks 156 54 FOREIGN PATENTS 82,378 2/1953 Denmark.

VERLIN R. PENDEGRASS, Primary Examiner 

